This invention relates to the art of fastening devices and, more particularly, to a fastening device for securing, supporting, depending, or otherwise attaching a component or fixture to a securing member and having access from only one surface thereof, in such instances as a relatively frangible ceiling, wall, hollow core door, shell construction, or as often found in stronger, double-walled compartments, bulkheads, and framing channels. The latter limiting characteristic is commonly known as a "blind hole" application; this term is used herein in such context. A long-standing problem has been to devise means whereby an adequate, secure fastening could be achieved in applications where making apertures large enough to permit manual access was impractical or prohibited, where fasteners have been installed after the initial construction or fabrication wherein inaccessible spaces were created, or wherever such surface attachment techniques were impractical or inappropriate, such as welding or brazing in flammable environments. The challenge to produce such fasteners has been complicated by the inclusions of such considerations as cost, both of materials and of production; efficacy; strength and dependability; and ease and speed of application.
A common problem encountered by housing construction workers, homeowners, and repairmen is that of securing fixtures and related hardware to surfaces and partitions that have a hollow portion between spaced support or framing members, such as ceilings, interior walls, fascia areas, and like structural forms. Aircraft, auto, ship, boat, construction industry, and retrofitting applications produce a multiplicity of circumstances wherein a strong fastener is needed for use in a "blind hole" application. Typically, nails or screws will not hold securely in gypsum, thin plywood, plasterboard, fiberglass, or thin metal without using reinforcing materials of appropriate kind and thickness. Even for metal bulkheads, metal screws are not as secure as would be a fastener with a threaded nut on the obverse side of the member to which an attachment or application is made if the obverse side were accessible.
Prior art has approached these problems through applying the general conceptualization of the toggle bolt or anchor, the expandable anchor or sleeve, and the plate with hingedly connected legs or straps and a slip collar finalizing the connection. Each of the classes of devices is analyzed below, chiefly in terms of problems, disadvantages, and shortcomings when used, inasmuch as it is well recognized that they are widely used, although limited in their utility in many ways, as will be noted.
The typical toggle includes an elongated, threaded body element with a toggle, which can be threaded onto and advanced along the bolt shaft by its rotation. The toggle may vary in type: (a) wing type, (b) spring biased type, (c) gravity type, (d) plastic wing nut type, (e) molly type, and (f) elastomeric flip toggle type. Types (a), (b), (d), and (f) require considerable fabrication and complex assembly of a multiplicity of parts, causing them to be comparatively costly. All of the types necessarily entail the use of much longer bolts or screws passing through the ceiling or wall opening than those needed to achieve the same purpose where both sides of the same securing element are accessible, thereby increasing the comparative costs.
Articulated toggles, chiefly found in types (a), (b), and (d), are often disposed to be inherently weak at the point(s) of articulation, where they fail under the excessive force when overtightened or under the stress of heavy loads. Toggles with spring-biased arrangements, type (b), are subject to failure of the small springs, or of the long, thin springs of some configurations, which become twisted, skewed, or radically deformed near the completion of the tightening process.
Specially designed parts or constituent elements, especially for types (a), (b), (c)., and (f) would increase the costs of these fasteners. The expandable toggles in general use have also required specially designed threaded bolts. This has limited the choices of lengths and diameters, thus curtailing the amount of affective stress that can be applied to the connection thereto. Toggles, especially types (a), (b), and (d), also require a hole through which to pass that is approximately twice the diameter of the bolt, thereby presenting a significant reduction in the critical area upon which the toggle will be depressed. Older gravity types, (c), with affixed toggles require special treatment of the excess bolt remaining on the accessible side of the connection after the tightening, i.e., cut off, bent upward, capped, et cetera.
In vertical applications, e.g., in hollow walls, it is difficult to align the toggle with the vertical axis of the connected element to obtain thereby the maximum support that may be needed for heavy loads upon the device. Additionally, toggles with wings of thin, channel-shaped metal often cut into gypsum board and plaster, especially if overtightened, thereby substantially weakening the connection.
Those toggles of types (d), (e), and (f), whether comprised totally or in part of elastomeric materials, are necessarily limited in the stress to which they may be subjected in a given installation because of the inherent fragility of these materials. Additionally, some of these materials are of such recent development that their degradation parameters are still subject to verification.
With only a few exceptions, toggles are not reusable. In most instances, the bolt elements may be salvaged, but the toggles are deformed beyond repair, or they cannot be retracted or recaptured and are discarded inside the hollow space.
Anchor bolts and expansion sleeves, or sheaths, often are ineffective when used overhead, when used in very thin partitions, or when coupled against a direct stress exerted in the same direction as their longitudinal axes. The majority of these types also are not reusable. Additionally, they are difficult to remove in the event it is desired to repair the area of penetration and restore it to its original plane of finish.
The anchor assemblies comprised of an anchor plate with a pair of elongated leg members and slip collars for affixing them to the accessible surface of the application are limited in the maximum strength available in the leg members. Any fixture or attached hardware to be used with the fasteners must accommodate the size and the protrusion of the slip collar on the accessible surface. Additionally, the need to space the legs across the anchor plate limits the minimum size of the anchor, thereby requiring larger holes for applicability.
Finally, there is, perhaps, the overriding concern to be addressed relative to the several weak parts involved in currently available fasteners, especially those with several parts in one device, and the relatively fragile kinds of connections, attachments, or suspension points presented therewith for use in blind hole applications. To phrase it from a different perspective, there is still a need for a very strong unitary fastener for these purposes.